Change In Interlayer Spacing Research Articles

Thermal behavior analysis of two bentonite samples selected from China

The differences in structure and thermal behavior of two Chinese bentonites (X-1 and J-1) are analyzed by thermogravimetry (TG), derivative thermogravimetry (DTG), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectroscopy. The TG–DTG–DSC data indicated that two water molecular layers were present in the interlayer of the X-1 bentonite, but one water molecule layer in the interlayer of the J-1 bentonite. The mineralogy of the X-1 bentonite sample was determined as calcium montmorillonite, opal-CT (OCT), and quartz (Q), but that of the J-1 sample was determined as sodium montmorillonite, OCT, and Q. These results correspond to the TG–DTG–DSC data. The XRD and FT-IR spectra clearly show that the structural changes and dehydroxylation of these two bentonites occur when temperature is raised from 25 to 900 °C. The bentonite samples lose adsorbed and hydration water up to 300 °C, between 300 and 750 °C, and then the 2:1 layer structure completely collapses by rising the heating temperature from 25 to 900 °C. The dehydration is followed by the loss of intensity and evolution of the OH vibration bands and the change of interlayer spacing. The typical bands identified in the FT-IR spectra are similar for these two bentonites, but there are some differences in their positions and intensities. Dehydroxylation is followed by the decrease in intensity and position in the bands at 3620 and 910 cm−1, which is completed by 600 °C. The thermal behavior of these two bentonites was influenced by the impurities, ion substation, and the types of interlayer cations.

Electrochemistry of Cu0.5VOPO4·2H2O: A Promising Mixed Metal Phosphorous Oxide for Secondary Lithium based Batteries

Bimetallic mixed metal vanadium phosphorous oxide structures (MM'PxOy) have been the subject of much recent electrochemistry study. In analogy to silver vanadium phosphorous oxides, this study involves copper vanadium phosphorous oxide. Under galvanostatic discharge in lithium anode cells, the Cu0.5VOPO4·2H2O (CuVPO) material delivered ∼280 mAh/g to 1.5 V. Unlike silver vanadium phosphorous oxides, crystallographic evaluation indicated little structural change upon electrochemical reduction of CuVPO, with no significant change in interlayer spacing and no evidence of copper metal formation. Notably, secondary battery evaluation showed retention of ∼100 mAh/g at C/20 with little fade, a significant improvement under repeated cycling relative to a related silver based material.

Microstructure and process of intercalation of imidazolium ionic liquids into montmorillonite

Organically modified clays exhibit adsorption capacities for cations, anions, and nonpolar organic compounds, which make them valuable for various environmental technical applications. Research into organic molecule modified montmorillonite should place importance on studying the mechanism of the intercalation process. Herein a new kind of green and steady ionic liquid, 1-Hexadecyl-3-methylimidazolium chloride monohydrate (C16mimCl) has been chosen as the intercalant agent. We have investigated the process that C16mimCl is intercalated into Na-montmorillonite in aqueous solution under batch studies and molecular simulations. The C16mimCl intercalation has been found relatively fast with a large rate constant. The intercalation is driven by both cations exchange and negative charge on the layer surface. The process is affected by the initial concentration and pH value of the solution; the basal spacing is increased to 2.88nm after intercalation. Molecular dynamic simulation further reveals that the initial concentration of C16mimCl can influence its configuration in the interlayer, causing the change of interlayer spacing. Apart from the electrostatic interaction, the hydrophobicity of the organic molecule also plays an important role in the intercalation process. Overall, ionic liquid intercalated montmorillonite is a promising environmental composite material with broad application potentials such as chemical fiber and aviation.

Investigation of Vibration Properties of Multi-Walled Carbon Nanotubes

Based on an explicit van der Waals (vdW) model, which can reproduce the interaction between any two layers of multi-walled carbon nanotube (MWCNT) and is dependent on the change of interlayer spacing and on the tube radii, the vibration analysis of multi-walled carbon nanotubes is carried out by using of the multi-layered Flugge shells model. The natural frequencies are analyzed in detail for with various radii and number of tubes. Furthermore, the natural frequencies of double-walled carbon nanotube with the innermost radii of 0.6 nm predicted based on the Flugge shell model are well compared with those from the Donnell shell one. The present investigation will be meaningful for the design and application of multi-walled carbon nanotubes as nano- resonators.

Rigorous van der Waals effect on vibration characteristics of multi-walled carbon nanotubes under a transverse magnetic field

An analytical method is presented to investigate rigorous van der Waals interaction effect on vibration characteristics of multi-walled carbon nanotubes embedded in matrix under a transverse magnetic field. Each of the concentric tubes of multiwall carbon nanotubes is considered as an individual elastic shell and coupled with any two walls through a rigorous van der Waals interaction being dependent on the change of interlayer spacing and the radii of tubes. Results show that the rigorous van der Waals interaction effect makes the lowest magneto-vibration frequency of multi-walled carbon nanotubes decrease and the highest magneto-vibration frequency increase. The effect of rigorous van der Waals interaction on magneto-elastic vibrations of multi-walled carbon nanotubes is dependent on the transverse magnetic strength and the matrix constrained stiffness.

Characterisation of organoclays and adsorption of p-nitrophenol: Environmental application

Organoclays were synthesised through ion exchange of a single surfactant for sodium ions, and characterised by a range of method including X-ray diffraction (XRD), BET, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM). The change in surface properties of montmorillonite and organoclays intercalated with the surfactant, tetradecyltrimethylammonium bromide (TDTMA) were determined using XRD through the change in basal spacing and the expansion occurred by the adsorbed p-nitrophenol. The changes of interlayer spacing were observed in TEM. In addition, the surface measurement such as specific surface area and pore volume was measured and calculated using BET method, this suggested the loaded surfactant is highly important to determine the sorption mechanism onto organoclays. The collected results of XPS provided the chemical composition of montmorillonite and organoclays, and the high-resolution XPS spectra offered the chemical states of prepared organoclays with binding energy. Using TGA and FT-IR, the confirmation of intercalated surfactant was investigated. The collected data from various techniques enable an understanding of the changes in structure and surface properties. This study is of importance to provide mechanisms for the adsorption of organic molecules, especially in contaminated environmental sites and polluted waters.

Modification of surface functionality and interlayer spacing of multi-walled carbon nanotubes using γ-rays

The surface functionality and interlayer spacing changes induced by γ-ray irradiation were investigated in multi-walled carbon nanotubes (MWCNTs). The modification effect of MWCNTs irradiated in air and epoxy chloropropane (ECP) was characterized by x-ray photoelectron spectroscopy, Raman spectroscopy, and x-ray diffraction. The results indicated that γ-ray irradiation in two different media improved the amount of oxygen-containing functional groups on nanotube surface, and the irradiation in ECP was more efficient. Compared with the pristine MWCNTs, the MWCNTs irradiated in air exhibited a decrease in width of G band and intensity ratio of D to G band in the Raman spectra and an increase in intensity and diffraction angle of (002) characteristic x-ray peak. However, the MWCNTs tended to show the opposite behaviors in Raman spectra and x-ray diffraction patterns after they were irradiated in ECP. This preliminary study suggests that γ-ray irradiation in air can meaningfully decrease the interlayer distance of MWCNTs and improve the graphitization of MWCNTs, while irradiation in ECP disorders and breaks the structure of MWCNTs. It is worth expecting that MWCNTs can be functionalized by γ-rays in reactive liquid and also be employed for preventing γ-ray radiation from reaching sensitive materials at least for short term experiments in air.

Dynamic buckling of double-walled carbon nanotubesunder axial impact loading

Using the modified finite element method, the nonlinear shell-spring finite element model is established with taking the van der waals force into account. Based on the B-R motion criterion, the dynamic bucking behaviors of multi-walled carbon nanotubes are examined systemically. The dynamic critical loads for buckling and failure of double-walled carbon nanotubes under axial impact load are obtained. It is shown that in the dynamic buckling process of multi-walled carbon nanotubes, the deformation of each wall is harmonious to each other and the change of interlayer spacing is very small. The magnitude and the duration of impact load as well as the length of carbon nanotube have greater effects on the dynamic buckling of carbon nanotubes. For the shorter carbon nanotubes, asymmetrical buckling mode appears earlier. The simulations further show that the stress wave propagation in carbon nanotubes induces the asymmetrical buckling mode. In the dynamic buckling process of carbon nanotubes, there are four circumferential lobes that can be observed obviously, and their wave crest and trough of the lobes change alternately.

Effects of organo‐clay modifier on physical–mechanical properties of butyl‐based rubber nano‐composites

AbstractBladders are important rubber parts used for shaping and curing of tires. These parts are exposed to high temperature, high pressure, medium‐large extension, and oxidative aging during their service life. Curing bladders are usually made of butyl‐based rubber compounds vulcanized with phenolic resin vulcanization systems. To study the effect of Montmorillonite nano‐clay on properties of these rubber parts and their functionality during service, the most compatible and well dispersed organically modified Montmorillonite (OMMT) nano‐clay has to be selected. To study the effects of organic modifier on properties of these compounds, five types of commercial OMMT were mixed with the compounds using the melt intercalation method. Effect of modifiers on compatibility between clay and rubber, dispersion of clay in the polymer matrix, and thus mechanical properties of the nano‐composite were studied by X‐ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), mechanical tension, and dynamic‐mechnical‐thermal analysis (DMTA). XRD results revealed an intercalated structure for all OMMTs, but with different degrees of rubber intercalation. The largest change in interlayer spacing of silicate layers due to intercalation of rubber was seen for an OMMT modified by dimethyl‐benzyl‐hydrogenated tallow, quaternary ammonium. AFM and SEM micrographs of the latter compound confirmed the intercalated structure with a good distribution of filler. Viscoelastic properties obtained from DMTA confirmed more compatibility between butyl‐based rubber compound and this OMMT. This modified clay was selected as the filler of choice for potential application in actual bladder compound. Uni‐axial tension tests could also differentiate among nano‐composites reinforced with differently modified clays. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Preparation and properties of natural nanocomposites based on natural rubber and naturally occurring halloysite nanotubes

A ‘green’ composite based on natural halloysite nanotubes (HNTs) and natural rubber (NR) was prepared by mechanical mixing. A silane coupling agent, bis (triethoxysilylpropyl)-tetrasulphide, was utilized to enhance the properties of these composites. It was observed that the reinforcing activity of HNTs was superior to commercial silica coupled with the same amount of silane coupling agent. Moreover the on-set thermal degradation decomposition temperature was improved by ∼64 °C with the addition of 10 parts HNTs per hundred of rubber. Transmission electron microscopic images confirmed the good dispersion of the HNTs in the rubber matrix, whereas X-ray diffraction studies showed a little change in interlayer spacing between the two silicate layers of HNTs.

Bias voltage inducedn- top-type transition in epitaxial bilayer graphene on SiC

We show by extensive first-principles calculations that an $n$- to $p$-type transition in epitaxial bilayer graphene can be induced by applying bias voltage on C-terminated SiC substrate, but cannot occur on Si-terminated SiC. Bias voltage can cause enough charge transfer between top and bottom graphene layers on C-terminated SiC to shift the Dirac level below or above the Fermi level. On both C- and Si-terminated SiC, change in interlayer spacing of the epitaxial bilayer graphene produces charge redistribution that leads to large increase in the energy gap, but cannot raise the Dirac level efficiently. The surface terminated condition or properties of substrate are of essential importance in possible gate tuning electronic behavior of epitaxial graphene on it.

Buckling analysis of multi-walled carbon nanotubes under combined loading considering the effect of small length scale

The torsional and axially compressed buckling of an individual embedded multi-walled carbon nanotube (MWNTs) subjected to an internal and/or external radial pressure was investigated in this study. The emphasis is placed on new physical phenomena which are due to both the small length scale and the surrounding elastic medium. Multiwall carbon nanotubes which are considered in this study are classified into three categories based on the radius to thickness ratio, namely, thin, thick, and almost solid. Explicit formulas are derived for the van der Waals (vdW) interaction between any two layers of an MWNT based on the continuum cylindrical shell model. In most of the previous studies, the vdW interaction between two adjacent layers was considered only and the vdW interaction among other layers was neglected. Moreover, in these works, the vdW interaction coefficient was treated as a constant that was independent of the radii of the tubes. However, in the present model the vdW interaction coefficients are considered to be dependent on the change of interlayer spacing and the radii of the tubes. The effect of the small length scale is also considered in the present formulation. The results show that there is a unique buckling mode (m,n) corresponding to the critical shear stress. This result is obviously different from what is expected for the pure axially compressed buckling of an individual multi-walled carbon nanotube.

The preparation and properties of sodium and organomodified-montmorillonite/polypyrrole composites: A comparative study

Two montmorillonites, an inorganic sodium montmorillonite (NaMMT) and an organo-modified montmorillonite (OMMT), were used for the preparation of montmorillonite/polypyrrole (MMT/PPy) composites. MMT particles were modified by the in situ polymerization of pyrrole in water, in aqueous solution of dodecylbenzenesulfonic acid (DBSA) used as anionic surfactant, and in water/methanol. Ferric chloride was used as oxidant in each case. Wide angle X-ray scattering (WAXS) measurements proved the intercalation of PPy into the galleries of NaMMT regardless the reaction media. In contrast, for OMMT/PPy composites, the increase of interlayer spacing depends on the preparation conditions, the highest increase in interlayer spacing was achieved in water/DBSA solution. The WAXS patterns of OMMT/PPy composites synthesized in methanol/water showed no change in interlayer spacing and the electrical conductivity of these composites was low, similar to that of NaMMT/PPy composites prepared under the same conditions. Conductivity about 1.1 S cm −1 was reached for OMMT/PPy composites containing 13.3 wt% PPy prepared in the presence of DBSA. The NaMMT/PPy composite containing 15.6 wt% PPy and prepared under the same conditions showed a conductivity of 0.26 S cm −1. X-ray photoelectron spectroscopy (XPS) proved that the surface of NaMMT/PPy composites is rich in MMT, whereas more PPy was found on the surface of OMMT/PPy composites. The conductivity of composites correlated with the N/Si atomic ratio determined from XPS results, which was taken as a semi-quantitative measure of the PPy surface fraction.

Torsional Buckling of Multi-walled Carbon Nanotubes Subjected to Torsional Loads

The torsional buckling of an individual multi-walled carbon nanotube under two different loading conditions is studied in this article. The multiple shell model is adopted and the effects of van der Waals forces between adjacent nanotubes are taken into account. An examination with an individual double-walled carbon nanotube shows that the effect of the change of interlayer spacing on the torsional buckling force can be neglected if only the innermost radius is larger than a certain value. Under this condition, single buckling equations are derived and explicit formulas for the critical torsional loads in terms of the buckling modes are obtained. It is found that the critical torsional load of a multi-walled carbon nanotube with torque exerted on the outermost tube is higher than that of the same multi-walled carbon nanotubes under the torques being proportionally applied to each individual layer of the multi-walled carbon nanotubes. For thin multi-walled carbon nanotubes with large radii, the critical torque linearly scales with its thickness, but the critical shear force (per unit length) of the multi-walled carbon nanotubes uniformly twisted along the cross section does not increase as its layer number (thickness) increases, which is due to the interlayer slips between adjacent nanotubes.

Thermal Buckling of Multi-Walled Carbon Nanotubes Based on a Rigorous van der Waals Interaction

This paper reports the result of an investigation on the axially compressed buckling of multi-walled carbon nanotubes under thermal load, based on a rigorous van der Waals interaction which is dependent on the change of interlayer spacing and the radii of tubes. From the point of view of continuum modeling, each of the concentric tubes of multi-walled carbon nanotubes is considered as an individual elastic shell and coupled with any two tubes through a rigorous van der Waals interaction force. Based on this model, some example calculations are carried out to describe the effect of temperature changes and van der Waals interaction models on the axially critical load of multi-walled carbon nanotubes. Some results obtained show that the axial buckling stress of multi-walled carbon nanotubes under thermal environment is dependent on the wave number of axially buckling modes, and the wave numbers corresponding to the minimum axial stress are not unique for the multi-walled carbon nanotubes under thermal environments. On the other hand, a rigorous van der Waals interaction force can make the axially critical load of multi-walled nanotubes under thermal loading increase. The effect of thermal environments on the axially critical stress of multi-walled nanotubes gradually increases as the axial half wavenumber (m) of buckling modes increases.

Reversible Change of Interlayer Spacing of Layered Double Hydroxides Containing Organic Carboxylates

Layered double hydroxide (LDH) has positive charge between the layers and is known as anion exchangeable clay being able to intercalate various organic and inorganica nions. In this study, organic-inorganic layered nanohybrids were prepared by intercalation of organic carboxylate anions into Zn/Al LDH in an aqueous solution. Four intercalation compounds were prepared by the reactions of succinate, terephthalate, 4-pyridinecarboxylate, and p-hydroxybenzoate anions with Zn/Al LDH in aqueous solution. Interlayer spacing of these four intercalation compounds decreased by the thermal treatment at 363 K, and recovered by the treatment in water, reversibly.

Effects of atomic relaxation and the electronic structure of niobium (100) and (110) surfaces

A comparative analysis of the atomic relaxation and electronic structure of niobium (100) and (110) surfaces has been carried out using the VASP-PAW method. The relaxation-induced changes in interlayer spacings of surface layers demonstrate an oscillating behavior but they substantially differ for the two analyzed surfaces; namely for the (110) surface with the closest atomic packing two outermost surface layers are contracted by 4.3% and the relaxation becomes noticeable for three outer layers, while for the more “open” (100) surface these quantities equal 13.1 and six layers, respectively. An analysis of the layer-by-layer distribution of the densities of states, spatial distribution of the charge density, and densities of states at the Fermi level indicates that the most considerable changes near Fermi level take place for (100) surface.

Swelling of a mesostructured zirconium oxide film

The structural changes that cause the change in interlayer spacing of a surfactant-templated zirconium oxide film have been studied using neutron diffractometry. We report that the film after drying on a glass substrate swells slightly through the addition of benzene by up to 4 Å on a lattice parameter of about 36 Å. The (0 0 1) and (0 0 2) diffraction peak widths, positions and areas of a swollen film were monitored as a function of benzene desorption. Disorder of the lamellar mesophase is considered as a cause of the observed effects on the diffraction signals.

Preparation and characterization of surfactant-free polystyrene/layered double hydroxide exfoliated nanocomposite via soap-free emulsion polymerization

The soap-free emulsion polymerization has been applied for preparing the surfactant-free polystyrene/layered double hydroxide exfoliated nanocomposite. The XRD and TEM determinations have been used to monitor the changes of interlayer spacing and morphology during polymerization. The results show that the obtained nanocomposite has the homogeneous structure of polymeric and inorganic components. Due to the absence of organic surfactant, the PS/LDH nanocomposite shows a remarked improvement on the onset decomposition temperature compared with virgin PS.

Radial breathing vibration of multiwall carbon nanotubes based on a rigorous van der Waals interaction

This paper reports the results of an investigation on radial breathing vibrations of multiwall carbon nanotubes (MWNTs) embedded in an elastic matrix, based on a rigorous van der Waals (vdW) interaction which is dependent on the change of interlayer spacing and the radii of tubes. Each of the concentric tubes of MWNTs is considered an individual elastic shell and coupled with any two tubes through a rigorous vdW interaction force. The matrix surrounding MWNTs is considered a spring in which the spring coefficient is defined by the Winkler model. The results obtained show that the radial breathing frequencies of the first vibration mode increase monotonically as the stiffness of the matrix increases. The matrix surrounding MWNTs not only changes the value of amplitude ratios between any two tube walls of the MWNTs embedded in an elastic matrix, but also changes the vibration modes between the tube walls of the MWNTs from the coaxial vibration to the non-coaxial vibration. The new features and the meaningful numerical results in the present work on radial breathing vibrations of MWNTs embedded in an elastic matrix may be used as a useful reference for Raman scattering of light that can indirectly provide structural data on nanotubes.